Answers to: pseudo-mip much faster than continous lphttp://www.or-exchange.com/questions/12619/pseudo-mip-much-faster-than-continous-lp<p>Continued there: <a href="https://www.ibm.com/developerworks/community/forums/html/topic?id=1ceca39b-c16a-460e-8f63-a5b3b487bfc5">Forum: CPLEX Optimizers pseudo-mip much faster than continous lp </a></p>
<p>Have an lp which is originally not a mip. when solving with simplex or network (using cplex), it takes about 1 Minute. When adding dummy integer 0..1, then cplex treats it as mip, solves the root-relaxation within a few seconds, and because solving the mip then is trivial, the problem is solved this way very fast. This is almost always the case.
So my question is: How does mip parametrize the root-relaxation, so that it is so much faster? I use both for mip root-algo and the continous problem the same solver (e.g. network, or simplex), so I would assume the root-relaxation in mip and the solution of the continous case should take the same time. Or does mip use (some internal) callback of the network/simplex-solver to stop the relaxation, when the solution is "good enough"? From where does it know then what's good enough (know the theoretical objValue)?</p>enFri, 18 Oct 2019 18:21:31 -0000